Spread Spectrum Digital Modem?

GlassWalkerTheurge asks: "I was wondering if anyone is aware of any spread spectrum digital modem technology that would make a mobile location (i.e. car, etc.) able to create a secure link to a ground station (i.e. home etc.) using multiple (say 4) digital cell phones on both ends. The traffic would be encrypted and spread over the 4 digital modems according to an algorythm available to both sides (negotiated when the secure link is established.) If it does not exist, anyone know if it is doable? I was thinking using a hardware encryption based on a periodically changed key (physical card?) that contained a 4096 bit key (software encryption type). An idea for my dream car."